Allowable point load to existing post tensioned concrete slab 1

shacked · Sep 20, 2017

I am located in Southern California and I am working on a single story residential remodel project. The house was built in 1984 and the concrete slab is post tensioned verified by the post tensioned slab note posted in the garage.

So I realize that there are many factors that determine the allowable point loads to a p.t. slab but I am just looking for some input as to an acceptable max point load that you would feel comfortable allowing at an interior portion of a p.t. slab for single story residential construction.

Basically the owner is eliminating a bearing wall and I am supporting the roof and ceiling framing with 2 new beams as to open up the area. There will be two new interior posts one with a total point load of 3.0kips dead & roof live load & the other total dl & Lr = 4.5kips.

I seem to remember another engineer telling me that a point load to a p.t. concrete slab for residential construction in S-Calif under 6 kips would be acceptable, but I am not 100% sure.

DETstru · Sep 20, 2017

Slabs on grade (regardless of PT or mild reinforcing) can take pretty significant point loads. The real determining factor is the thickness and the properties of the soil below.

Here's a good article:

http://www.structuremag.org/wp-content/uploads/2014/08/C-StructuralDesign-Azzi-Apr081.pdf

shacked · Sep 21, 2017

Thanks for the information DET. The only problem is that there is no soils report since this is such a minor remodel so I would not have any idea of the soil modulus of subgrade rxn.

DETstru · Sep 21, 2017

Given that your load is so small I wouldn't be concerned with assuming a low modulus of subgrade reaction and calling it good.

You can look at other buildings or reports that you've seen nearby or maybe contact a geotech to see what they think of the area. If your load was 10x what you're thinking about I'd go through with some investigation.

Since you're in California, I'd be more worried about losing a portion of your lateral load resisting system. Is that bearing wall a shear wall?

shacked · Sep 22, 2017

Thanks DET. Well, the wall is a bearing wall supporting the ceiling and a few ceiling beams that support a portion of the ridge. It isn't lateral resisting as the studs do not extend all of the way up to the underside of the roof rafters.

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Allowable point load to existing post tensioned concrete slab 1

shacked

Structural

DETstru

Structural

shacked

Structural

DETstru

Structural

shacked

Structural

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